The present invention relates to power supplies in general, and, more particularly, to high-efficiency DC-to-DC converters, switching regulators, and tracking power-supplies.
DC-to-DC converters are widely used today in many applications. Many of the efficient implementations are based on switching capacitors, and sometimes also inductors, and are referred to as switching regulators. Switching regulators that are based on capacitors only are becoming more popular since inductors are practically inconvenient for use especially where miniaturization and EMI is of concern.
Prior art switching regulators uses a two phase cycle. A charge-phase during which capacitors are charged while not being connected to the load, and a discharge-phase during which capacitors are discharged trough the load.
One problem associated with prior art switching regulators is that specific design parameters can only reach high efficiency within a relatively narrow range of output current and/or voltage requirements for applications where output current or voltage are changing significantly the efficiency of prior art switching regulators drops significantly.
Prior art methods to improve the ability to cope with a wide range of voltage/current requirements includes controlling the duty cycle between the charge and discharge phases, and/or controlling the resistance trough which the capacitors are charged during the charge-phase.
Another limiting factor of prior art implementations is that during the charge-phase there is power loss due the changing of the capacitor, that is proportions 1 to xcex94V*C.
In order to keep supplying power during the charge-phase, an output-capacitor is always connected at the output in parallel to the load. This output-capacitor needs to be charged to a voltage higher than the desired output voltage during the discharge-phase, so that it can keep supplying power during the charge-phase. This increases the ripple at the output of the power supply.
Another problem of current switching regulators is that the frequency content of the ripple (noise) at the output is dictated by the switching regulator circuit, and the power consumption, and can not be controlled to provide a noise frequency content that is more suitable for specific applications.
There is thus a widely recognized need for, and it would be highly advantageous to have, a high-efficiency power supply, that is capable of supporting a wide range of voltage/current requirements, while having low ripple with a controlled frequency content. These goals are met by the present invention.
[1] EP0998795, WO9905806 xe2x80x9cMethod and apparatus for performance improvement by qualifying pulses in an oversampled, noise-shaping signal processorxe2x80x9d
[2] EP0906659, WO9749175 xe2x80x9cOversampled, noise-shaping, mixed-signal processorxe2x80x9d
[3] xe2x80x9cRelationships between Noise Shaping and Nested Differentiating Feedback Loopsxe2x80x9d, by J. Vanderkooy, and M. O. J. Hawksford, Journal of the Audio Engineering Society, Vol. 47, No. 12, November 1999.
Tracking Power Supplyxe2x80x94A power supply capable of providing a variable output voltage. According to the present invention, an efficient tracking power-supply is implemented, having control logic controlling a network of switching capacitors. By controlling the switches, different network connections can be made, giving rise to different electrical circuits. This allows creating multiple supply voltages with high efficiency at the load terminals, and monitoring voltages through the sensor terminals.
Multi-Level Quantizerxe2x80x94The above tracking power-supply can be viewed as a quantizer (a xe2x80x9cmulti-level quantizerxe2x80x9d) with multiple output levels possible during different time intervals, where the level changes during each time interval according to the voltages on the capacitors.
Network of Switched Capacitorsxe2x80x94the network of switches and capacitors used in the tracking power-supply.
Network Connectionxe2x80x94This is a specific set of connections, created by controlling the switches of the network of switched capacitors. This set of network connections creates an electrical circuit involving some or all of the capacitors, supplies, load terminals and sensor terminals.
Network Statexe2x80x94The state of the network of switched capacitors at a certain time. The voltages across the capacitors define the network state.
1-Bit Statexe2x80x94a specific case of a network state where a 1-bit state per capacitor indicates whether the voltage over it is higher or lower than some target voltage. This is useful when implementing the targeted capacitors selection algorithm.
Sensorxe2x80x94A sensor is any means of monitoring the network state while causing minimal affect. To monitor voltage over a certain capacitor, an appropriate network connection can be made by the control logic. A sensor for the 1-bit state can be the output of a comparator, comparing the voltage over the capacitor to the target voltage.
Estimated Network Statexe2x80x94An estimated network state is a network state where some or all of the capacitor voltages are estimated rather than directly monitored.
Network Parametersxe2x80x94The network parameters include sufficient information about components involved in the network of switched capacitors. By way of example, this information may include electrical parameters of the load and main supplies, the capacitance of each capacitor, and the time intervals, whether absolute or relative. In certain embodiments of this invention, the control logic may need to know methods parameters in order to estimate, or predict, the estimated network state when direct monitoring is not feasible. The network parameters may be supplied to the control logic, or may be measured by the control logic through the sensor, whether during initialization time, during operation, or both.
Time Intervalxe2x80x94A period of time during which the network connection is held fixed. The duration of such time intervals may be constant or variable, depending on the application.
Load Time Intervalxe2x80x94A time interval during which the network connection involves the tracking power-supply output terminals.
Monitoring Time Intervalxe2x80x94A time interval during which monitoring of the network state can be performed. A monitoring time interval can overlap a load time interval.
Control Logicxe2x80x94Logic controlling the network of switched capacitors via the switches, in order to create a desired network connection. The main task of the control logic is to determine the best network connection involving the load at any time interval. The control logic implements a selection algorithm, and attempts to minimize the value of the target function, while conforming to some other criteria. The control logic may be implemented fully in the digital domain, while monitoring the state of the network of switched capacitors through the sensor. Alternatively, the control logic can be implemented in the analog domain. The control logic unit has one or more inputs and one or more control outputs.
Target Functionxe2x80x94At each load time interval, there is an ideal desired output from the tracking power-supply. Since in general the tracking power-supply cannot provide this output exactly, the target function is a xe2x80x98costxe2x80x99 function that associates a cost with each possible output from the tracking power-supply during the current load time interval. The control logic uses this function as part of the selection algorithm to determine the best network connection for the current load time interval.
Selection Algorithmxe2x80x94The selection algorithm applied by the control logic tries to minimize the target function, while applying additional considerations as well. Such considerations can be of different natures, including, without limitation, minimizing the number of switching operations taking place, keeping voltages on capacitors within certain ranges, keeping voltages on capacitors close to a target voltage, maintaining certain characteristics of the power stage, and so forth.
Constrained Capacitorsxe2x80x94A selection algorithm according to which each capacitor has a target voltage range, and where the capacitor is not allowed to be connected such that it would charge when the voltage across it is above its target voltage range, and vice versa.
Targeted Capacitorsxe2x80x94A selection algorithm according to which each capacitor has a target voltage, and where the capacitor is not allowed to be connected such that it would charge when the voltage across it is above its target voltage, and vice versa.
Target Errorxe2x80x94The error, in the case of the targeted capacitor selection algorithm, of the actual average voltage supplied by a capacitor during a load time interval relative to that capacitor""s target voltage.
Power Stagexe2x80x94The final stage of the power supply. Embodiments of the present invention describe a linear power stage and a discrete power stage.
Linear Power Stagexe2x80x94A power supply according to the present invention having an analog voltage regulator as the final power stage, where the power-supply is a tracking power-supply. The advantage of this approach is that it reduces the noise generated by the tracking power-supply at the final output.
Discrete Power Stagexe2x80x94A power supply according to the present invention having no analog power stage, where the tracking power-supply is connected directly to the power supply output, and acts as a Multi-Level Quantizer. In this approach, the noise-shaping loop handles all noise. No linear-analog power components are used, and this is an advantage in certain cases.
Noise-Shaping Loopxe2x80x94A feedback and filtering network that causes the noise energy (whether non-linear errors correlated with the input, or uncorrelated noise) to reside in frequencies where the noise poses no problem. In one embodiment of the present invention, the noise-shaping loop may be implemented entirely in the analog domain, around the power stage. Alternatively, in another embodiment of the present invention, the noise-shaping loop may be implemented entirely in the digital domain before the power stage, based on information supplied by the control logic. In yet another embodiment, the noise-shaping loop may be implemented as a hybrid digital-analog domain using an A-to-D converter to convert analog feedback from the output of the power stage into the digital domain.
Linear Quantizerxe2x80x94The Selection algorithm described in xe2x80x9c2*N+3 Level Quantizer using N Capacitors and the Targeted Capacitors Selection Algorithmxe2x80x9d below.
Binary Quantizerxe2x80x94The Selection algorithm described in xe2x80x9c1+2(N+1) Level Quantizer using N Capacitors and the Targeted Capacitors Selection Algorithmxe2x80x9d below.
Conversion Ratioxe2x80x94The ratio of the voltage desired at the output of the power supply, to the voltage of the main power supply.
The main goal of the present invention is to improve the efficiency performance of switching power supplies, in order to reduce electrical power consumption. Another goal is to support a wider range of output current/voltage requirement with the same power supply, while maintaining the efficiency. Another goal is to better control the frequency content and amplitude of the ripple at the output of the power supply. Another goal is to provide, for a power supply that can track fast changes in output voltage requirements, thus implementing an efficient tracking power supply. Yet another goal is to provide for a power supply that can regulate a main power source that is not stable.
According to the invention, a network of switches and capacitors is used to create a desired voltage at the load terminals of a power supply, by configuring different circuits between the load terminals involving one or more of the main power supplies and the capacitors.
A novel aspect of this invention is that the circuits are arranged such that capacitors will always charge and/or discharge trough the load, thus eliminating the need for a charge-phase that is not involving the load. Because both charging and discharging of the capacitors is done trough the load, and involving the same load current, the amount by which capacitors are charged and discharged is automatically balanced eliminating the need to specifically control the durations of charge and discharge phases, and the resistance during charge phases.
Another novel aspect of the present invention is the use of an integral feedback control and noise-shaping unit to control the frequency content of the switching noise and ripple at the output.
This innovation describes a tracking power-supply that is easy to design as well as inexpensive to manufacture and use, and which is well-suited for integrated circuitry.
Two major applications are treated in this invention.
First application is where conversion with a fixed Conversion Ratio from a main power source is desired.
Second application is where conversion with a variable Conversion Ratio from a main power source is desired, weather the desired output voltage changes, or the main supply voltage is changing, or both are changing.
Four different types of embodiments are described according to this invention. All embodiments use the Network of Switched Capacitors as the mains to provide a desired level at the output. The differences between the different embodiments are in the use of other supporting circuitry such as an analog linear regulator stage, and noise-shaping feedback loop.
In some embodiments the output from the Network of Switched Capacitors is used directly as the output in other embodiments a feedback noise shaping loop from the output is used to control the frequency content of the ripple and noise at the output of the Network of Switched Capacitors. In other embodiments a linear regulator is connected to the output of the Network of Switched Capacitors to regulate the ripple and noise at the output. Other embodiments uses both linear regulator as well as a noise shaping feedback loop.
An embodiment example of a Networks of Switched Capacitors with output voltage that is always reference to a common ground, is shown in FIG. 5.
In many cases of a power supply only one, or few. DC output voltage is required, rather than any output voltage. Thus the complexity of the Network of Switched Capacitors can be significantly reduced, compared with that needed to support a generic tracking power supply.
FIG. 1 is a general block diagram illustrating the basic configuration of a power supply according to the invention, that is suitable for supplying an output voltage that is within a fixed Conversion Ratio to a main power source.
The main power source 101, is connected to the Network of Switched Capacitors 102, that provides the output voltage trough the load terminals 103 (L+, Lxe2x88x92). A control logic 104 is controlling the switches of the Network of Switched Capacitors trough the Control outputs 105, and according to the Sensor inputs 106 from the Network of Switched Capacitors. Since the Conversion Ratio of the output voltage to the main power source is fixed, no control input is needed to control the output voltage, rather the control logic creates the Network Connections to always provide for the same Conversion Ratio at the load terminals.
In the embodiment of FIG. 1, the output will have ripple whose amplitude is dependent on the capacitance of capacitors in the Network of Switched Capacitors, the switching frequency, and the current consumed by the load. As explained above, because the capacitors both charge and discharge by the same current that is consumed by the load, the ripple will always be optimal for the given parameters. The frequency content of the ripple is not controlled in this embodiment.
Since a constant Conversion Ratio to the main power supply is needed at the load terminals, the most efficient Selection Algorithm can be determined by which method provides the closest Conversion Ratio to the desired one, with the most efficient network. For example if the desired Conversion Ratio is 1/3 or 2/3, the most efficient selection algorithm will be the Linear Quantizer, where N=2. If for example the desired Conversion Ratio is 1/4, or 3/4, the most efficient selection algorithm will be the Binary Quantizer, with N=2.
It is also possible to recursively combine several Linear Quantizers and Binary Quantizers in order to achieve efficient Networks that will provide ratios that are multiples of the individual ratios of each Network. This is done recursively by combining the Networks such that the output of one Network serves as the supply for another Network. For example, for a desired Conversion Ratio of m/9 (where m less than 9) two Linear Quantizers can be combined, the first with N=2 and Target Voltages 1/3 and 2/3, and the second with N=2 and Target Voltages of 1/9 and 2/9. A desired Conversion Ratio of m/12 (where m less than 12) can be achieved by combining a Linear Quantizers with N=2 and Target Voltages 1/3 and 2/3, and a Binary Quantizer with N=2 and Target Voltages of 1/(3*2) and 1(3*4).
In such embodiments the Network of Switched Capacitors consists of groups of capacitors and Target Voltages according to the Linear Quantizer or Binary Quantizer methods, where one group refers to the main power supply, and the other groups refer to one of the possible quantizer output levels of the former groups as it""s main power supply recursively. It can be proven similarly to the proof in Binary Quantizer below, that all such combinations are always possible to generate while conforming to the Targeted Capacitors Selection Algorithm.
Another embodiment of the current invention is shown in FIG. 2. This embodiment allows for a variable Conversion Ratio, by adding a control input to the Control Logic. The power supply according to the invention can act as a Tracking Power Supply, and track the control input.
Another embodiment of the invention is shown in FIG. 3. In this embodiment the main power supply is not stable, and the desired output voltage is a stable (regulated) DC voltage. A referenced voltage converter 308 is monitoring the main power supply voltage, and supplies it as the control input. The Control Logic will adjust the Conversion Ratio such that the output will remain stable at the desired output voltage. By way of example, the referenced voltage converter may consist of a network of resistors to divide the main power supply voltage, and an A-to-D converter with an internal absolute voltage reference.
FIG. 4, shows another embodiment of the invention where a noise shaper 108 and feedback loop is added around the power supply, and controls the output voltage trough the control input 107. The noise shaper 108 has a reference input 108A, this reference input is related to the desired output voltage, weather it is a constant DC voltage, or a variable voltage. The feedback from the load terminals is fed trough a buffer 108C to the feedback input 108B of the noise shaper 108. By having this feedback and noise shaping configuration few goals are achieved:
The power supply output voltage will not be sensitive to instabilities or noise of the main power supply thus it acts as a voltage regulator.
The frequency spectrum of the ripple and noise at the power supply output are controlled to reside in such frequencies where it will not pose a problem to the load for a given application.
A general reference for noise shaping loops in both the analog and digital domains is [3].
In another embodiment of this invention a linear voltage regulation can be added at the output of the Network of Switched Capacitors. This will further reduce ripple and noise of the power supply. The output voltage from the Network of Switched Capacitors can be adjusted to be close enough to the desired final output so that the power dissipation over the linear voltage regulator is small. To add a linear voltage regulator at the outputs of the embodiments of FIGS. 1 and 3 is straight foreword.
FIG. 5, shows a possible implementation of the Network of Switched Capacitors suitable for the Targeted Capacitors Selection algorithm that is capable of supplying an output voltage that is always referenced to a common ground. The main power supply has two supply terminals Vdd and Vss 501A and 501B respectively, where Vss is the common ground. One of the load terminals Lxe2x88x92 is permanently connected to Vss as the common ground. The comparators 501A-C provides the sensor inputs to the Control Logic, in this case these are 1Bit State signals. The network of switches and capacitors 502 allows for configuring any combination of sum and difference of the voltages over the capacitors by cascading any desired number of the available capacitors with the desired polarity. Using the switches 502A-D the load terminal L+ can be connected to have any of the following voltages with reference to Lxe2x88x92:
L+=A0Vdd+A1*C1+ . . . +An*Cn 
Where: A0, A1 are 0 or 1, and A2 . . . An are xe2x88x921 or 0 or 1, and C1 being the capacitor with the highest Target Voltage.
For those skilled in the art it is evident that when the desired Conversion Ratio requires only a subset of the possible above combinations, than switches that are never used can be omitted from the circuit of FIG. 5, in order to simplify it.
According to the present invention, the Network of Switched Capacitors approximates a Multi-Level Quantizer. In order to implement a Multi-Level Quantizer, it is necessary to generate multiple voltage levels. According to the present invention, an efficient way to generate multiple voltages from one power supply is by using the same network of switched capacitors as in the tracking power-supply previously described. The target function for the control logic in this case is simply to produce the level closest to the signal at the input of the Multi-Level Quantizer. Other constraints can be added in the control logic, as will be described below by way of a non-limiting example regarding the Constrained capacitor or targeted capacitors selection algorithms.
Therefore, according to the present invention there is provided a power supply receiving electrical energy from a primary source of electrical energy having a Vss source voltage and a Vdd source voltage, and supplying output power via load terminals, the power supply comprising a Network of Switched Capacitors containing at least one capacitor for storing electrical energy, such of said at least one capacitor having a voltage thereon, wherein said Network of Switched Capacitors is operative to configuring electrical circuits between said load terminals such that said at least one capacitor substantially charge or discharge trough said load terminals, and wherein said electrical circuits include voltages and components selected from a group containing a) the Vss source voltage, b) the Vdd source voltage, and c) a non-negative number of capacitors of said Network of Switched Capacitors.